[luatex] Poor Spacing in the \frac Environment

[Emil E]

Hello,
I'm typesetting some simple math problems/solutions using LuaLaTeX,
and I'm having trouble with the spacing between the numerator and
division bar in \frac environments.
I've attached a MWE below, along with an image showing the my
output of the MWE.
I apologize in advance if my image links don't follow the proper
etiquette for this mailing list.

\documentclass[11pt]{article}

\usepackage{amsmath,amsthm,amssymb,amsfonts}
\usepackage{fontspec}
\setmainfont[Ligatures=TeX]{TeX Gyre Pagella}
\usepackage{unicode-math}
\setmathfont{TeX Gyre Pagella Math}
\begin{document}
$$
\frac{xxxxxxLLLLLL}{xxxxxxTTTTTT} \frac{2(x-1)-(x^{2}-1)}{(x^{2}-1)(x-1)}
$$
\end{document}

Here is a screenshot of the PDF output on my system.
Note how the spacing between the bottom of the L and the division bar
is about 2-3x larger than the spacing between the top of the T and
division bar.
https://i.imgur.com/RWeuSVA.png

The bizarre spacing occurs regardless of font, or the packages
fontspec, unicode-math, or the AMS packages.
This seems to indicate that it's a problem with LuaLaTeX itself.
I've been able to fix the fraction spacing by defining a new \frac
environment that manually adjusts the spacing of the numerator,
but that's a "hacky" solution that I don't like using.
PDFLaTeX shows proper spacing using the same math code, however
I'd like to stay with LuaLaTeX instead of reverting to PDFLaTeX.

Is there any way to fix this spacing?

Below are some details of my set-up:
Arch Linux x64
Running TeXLive 2014, installed manually and up-to-date
LuaLaTeX version is beta-0.79.1 (TeX Live 2014) (rev 4971)
Compiling through TeXStudio 2.8.8
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://tug.org/pipermail/luatex/attachments/20150118/b1ea8a91/attachment.html>